1. Technical Field
Example embodiments of the present invention relate in general to a technology for tracking motion of an object by analyzing images of the object, and more particularly, to a method of extracting ridge data in a method of tracking motion of an object and an apparatus and method for tracking a joint motion of an object.
2. Related Art
Technology for tracking motion of an object plays a major role in kinesiology, human engineering, sports science, and the fields of computer vision, human-computer interaction, etc. Currently used methods of tracking motion of an object may be roughly classified as a tracking-based method and a learning-based method.
In the learning-based method, to estimate a posture of an object, motion of the object is generally defined by classification or regression. Then, training is performed using samples including labels, and the posture of the object is estimated using an acquired training model. However, with the learning-based method, it is impossible to acquire accurate estimation results because the classification enables only a crude estimation of the posture of the object and the regression is severely affected by the surroundings of the object.
On the other hand, in the tracking-based method, a posture of an object is estimated by one-pair matching between a current frame and a previous frame temporally consecutive in a video. This method shows a relatively high degree of precision in posture tracking within a short time.
Although much research is being conducted on tracking of an object's posture, it is difficult in practice to stably and continuously acquire an object's posture using a computer vision. There is a method of attaching markers that enable recognition of an object's major parts and tracking the object's posture based on the markers. However, the method involves special equipment, such as markers and a sensor, in addition to a camera, and thus cannot track an object's motion from general images.
Also, when some parts of an object are covered by other parts and it is not possible to acquire accurate data of the covered parts, image data of the covering parts is required to be removed so as to acquire the data of the covered parts. This is more so for humans. Parts of a human are covered by various clothes and natural motions, and thus tracking of a human's posture is considerably limited.
Due to flexibility of joints, a human body is not fixed in one posture and but is able to take various postures. A human easily senses various postures of a human body with naked eyes, whereas it is not easy for a computer to recognize a particular posture of a human body from images input to an image input device. In addition, since people have slightly different body structures, posture tracking should be performed in consideration of many people's various body structures.
Existing technology for solving these problems includes the aforementioned method of tracking the positions of markers to determine a posture of a human body, and a method of causing a light-and-shade image of a human body to be formed using predetermined lighting and receiving the light-and-shade image through an image input device to determine a posture. The method employing markers involves attaching light sensors on a human body. According to the method, three-dimensional (3D) coordinates of the light sensors are tracked using several cameras to determine a posture of the corresponding person. According to the method of determining a posture of a human body using predetermined lighting, light and shadow of a human body is acquired by an image input device using several lighting fixtures to determine a posture of the human body. These technologies for determining a posture of a human body are mainly applied to sensitive controllers of console game machines and used in martial arts games, dance games, and so on.
However, existing systems for determining a posture of a human body are limited by a specific lighting space or markers attached to a human body, and thus are inconvenient and inappropriate to determine a posture of the human body from general images. This is because it is not possible to measure a posture of a person unless the person moves in the specific lighting space or has markers attached to himself or herself.